bench - The Cargo Book

# cargo bench

## NAME

cargo-bench - Execute benchmarks of a package

## SYNOPSIS

`cargo bench [OPTIONS] [BENCHNAME] [-- BENCH-OPTIONS]`

## DESCRIPTION

Compile and execute benchmarks.

The benchmark filtering argument `BENCHNAME` and all the arguments following the two dashes (`--`) are passed to the benchmark binaries and thus to libtest (rustc’s built in unit-test and micro-benchmarking framework). If you’re passing arguments to both Cargo and the binary, the ones after `--` go to the binary, the ones before go to Cargo. For details about libtest’s arguments see the output of `cargo bench — --help`. As an example, this will run only the benchmark named `foo` (and skip other similarly named benchmarks like `foobar`):

    cargo bench -- foo --exact

Benchmarks are built with the `--test` option to `rustc` which creates an executable with a `main` function that automatically runs all functions annotated with the `#[bench]` attribute. Cargo passes the `--bench` flag to the test harness to tell it to run only benchmarks.

The libtest harness may be disabled by setting `harness = false` in the target manifest settings, in which case your code will need to provide its own `main` function to handle running benchmarks.

## OPTIONS

### Benchmark Options

--no-run

  Compile, but don’t run benchmarks.

--no-fail-fast

  Run all benchmarks regardless of failure. Without this flag, Cargo will exit after the first executable fails. The Rust test harness will run all benchmarks within the executable to completion, this flag only applies to the executable as a whole.

### Package Selection

By default, when no package selection options are given, the packages selected depend on the current working directory. In the root of a virtual workspace, all workspace members are selected (`--all` is implied). Otherwise, only the package in the current directory will be selected. The default packages may be overridden with the `workspace.default-members` key in the root `Cargo.toml` manifest.

-p SPEC…​
--package SPEC…​

  Benchmark only the specified packages. See cargo-pkgid(1) for the SPEC format. This flag may be specified multiple times.

--all

  Benchmark all members in the workspace.

--exclude SPEC…​

  Exclude the specified packages. Must be used in conjunction with the `--all` flag. This flag may be specified multiple times.

### Target Selection

When no target selection options are given, `cargo bench` will build the following targets of the selected packages:

- lib — used to link with binaries and benchmarks

- bins (only if benchmark targets are built and required features are available)

- lib as a benchmark

- bins as benchmarks

- benchmark targets

The default behavior can be changed by setting the `bench` flag for the target in the manifest settings. Setting examples to `bench = true` will build and run the example as a benchmark. Setting targets to `bench = false` will stop them from being benchmarked by default. Target selection options that take a target by name ignore the `bench` flag and will always benchmark the given target.

Passing target selection flags will benchmark only the specified targets.

--lib

  Benchmark the package’s library.

--bin NAME…​

  Benchmark the specified binary. This flag may be specified multiple times.

--bins

  Benchmark all binary targets.

--example NAME…​

  Benchmark the specified example. This flag may be specified multiple times.

--examples

  Benchmark all example targets.

--test NAME…​

  Benchmark the specified integration test. This flag may be specified multiple times.

--tests

  Benchmark all targets in test mode that have the `test = true` manifest flag set. By default this includes the library and binaries built as unittests, and integration tests. Be aware that this will also build any required dependencies, so the lib target may be built twice (once as a unittest, and once as a dependency for binaries, integration tests, etc.). Targets may be enabled or disabled by setting the `test` flag in the manifest settings for the target.

--bench NAME…​

  Benchmark the specified benchmark. This flag may be specified multiple times.

--benches

  Benchmark all targets in benchmark mode that have the `bench = true` manifest flag set. By default this includes the library and binaries built as benchmarks, and bench targets. Be aware that this will also build any required dependencies, so the lib target may be built twice (once as a benchmark, and once as a dependency for binaries, benchmarks, etc.). Targets may be enabled or disabled by setting the `bench` flag in the manifest settings for the target.

--all-targets

  Benchmark all targets. This is equivalent to specifying `--lib --bins --tests --benches --examples`.

### Feature Selection

When no feature options are given, the `default` feature is activated for every selected package.

--features FEATURES

  Space or comma separated list of features to activate. These features only apply to the current directory’s package. Features of direct dependencies may be enabled with `<dep-name>/<feature-name>` syntax.

--all-features

  Activate all available features of all selected packages.

--no-default-features

  Do not activate the `default` feature of the current directory’s package.

### Compilation Options

--target TRIPLE

  Benchmark for the given architecture. The default is the host architecture. The general format of the triple is `<arch><sub>-<vendor>-<sys>-<abi>`. Run `rustc --print target-list` for a list of supported targets.

  This may also be specified with the `build.target` config value.

### Output Options

--target-dir DIRECTORY

  Directory for all generated artifacts and intermediate files. May also be specified with the `CARGO_TARGET_DIR` environment variable, or the `build.target-dir` config value. Defaults to `target` in the root of the workspace.

### Display Options

By default the Rust test harness hides output from benchmark execution to keep results readable. Benchmark output can be recovered (e.g., for debugging) by passing `--nocapture` to the benchmark binaries:

    cargo bench -- --nocapture

-v
--verbose

  Use verbose output. May be specified twice for "very verbose" output which includes extra output such as dependency warnings and build script output. May also be specified with the `term.verbose` config value.

-q
--quiet

  No output printed to stdout.

--color WHEN

  Control when colored output is used. Valid values:

  - `auto` (default): Automatically detect if color support is available on the terminal.

  - `always`: Always display colors.

  - `never`: Never display colors.

  May also be specified with the `term.color` config value.

--message-format FMT

  The output format for diagnostic messages. Valid values:

  - `human` (default): Display in a human-readable text format.

  - `json`: Emit JSON messages to stdout.

  - `short`: Emit shorter, human-readable text messages.

### Manifest Options

--manifest-path PATH

  Path to the `Cargo.toml` file. By default, Cargo searches in the current directory or any parent directory for the `Cargo.toml` file.

--frozen
--locked

  Either of these flags requires that the `Cargo.lock` file is up-to-date. If the lock file is missing, or it needs to be updated, Cargo will exit with an error. The `--frozen` flag also prevents Cargo from attempting to access the network to determine if it is out-of-date.

  These may be used in environments where you want to assert that the `Cargo.lock` file is up-to-date (such as a CI build) or want to avoid network access.

--offline

  Prevents Cargo from accessing the network for any reason. Without this flag, Cargo will stop with an error if it needs to access the network and the network is not available. With this flag, Cargo will attempt to proceed without the network if possible.

  Beware that this may result in different dependency resolution than online mode. Cargo will restrict itself to crates that are downloaded locally, even if there might be a newer version as indicated in the local copy of the index. See the cargo-fetch(1) command to download dependencies before going offline.

  May also be specified with the `net.offline` config value.

### Common Options

-h
--help

  Prints help information.

-Z FLAG…​

  Unstable (nightly-only) flags to Cargo. Run `cargo -Z help` for details.

### Miscellaneous Options

The `--jobs` argument affects the building of the benchmark executable but does not affect how many threads are used when running the benchmarks. The Rust test harness runs benchmarks serially in a single thread.

-j N
--jobs N

  Number of parallel jobs to run. May also be specified with the `build.jobs` config value. Defaults to the number of CPUs.

## PROFILES

Profiles may be used to configure compiler options such as optimization levels and debug settings. See the reference for more details.

Benchmarks are always built with the `bench` profile. Binary and lib targets are built separately as benchmarks with the `bench` profile. Library targets are built with the `release` profiles when linked to binaries and benchmarks. Dependencies use the `release` profile.

If you need a debug build of a benchmark, try building it with cargo-build(1) which will use the `test` profile which is by default unoptimized and includes debug information. You can then run the debug-enabled benchmark manually.

## ENVIRONMENT

See the reference for details on environment variables that Cargo reads.

## Exit Status

0

  Cargo succeeded.

101

  Cargo failed to complete.

## EXAMPLES

1. Build and execute all the benchmarks of the current package:

       cargo bench

2. Run only a specific benchmark within a specific benchmark target:

       cargo bench --bench bench_name -- modname::some_benchmark

## SEE ALSO

cargo(1), cargo-test(1)